Surface density of synthetically tuned spinel oxides of Co3+ and Ni3+ with enhanced catalytic activity for methane oxidation

Spinel oxides containing Co and Ni are a promising substitute as a noble metal catalyst for methane combustion. Achieving a complete oxidation of methane under 400 degrees C remains challenging, and whether Ni3+ or Co3+ is the active center for the catalytic combustion of methane is a controversial issue. Therefore, we designed a series of spinel oxide catalysts by exposing different amounts of Ni3+ and Co3+ deposited on the surface by hydrothermal and co-precipitation methods in order to study the influence of high oxidation state (Ni3+ and Co3+) on surface and catalytic activity. The catalytic performance increased almost linearly with increasing Ni3+ + Co3+ on the surface of the catalyst. Thus, we are convinced that Ni" and Co" both act as active centers. The amount of Ni3+ + Co3+ on a hydrothermal 60 h NiCo2O4 nanosheet surface is the highest, and reveals the best catalytic performance with 7'50 (50% methane conversion) at about 280 degrees C. 10 vol% H2O added to the system has little impact on activity, especially at high space velocities due to the long hydrothermal time with less absorbed oxygen species and crystal defects. Overall, these results help clarify methane activation mechanisms and aid the development of more efficient low-cost catalysts. (C) 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.